1. Field of Invention
This invention is related to optical devices, particularly to optical devices having a compact structure.
2. Description of Prior Art
Optical devices are closely related to industry, medical field, and our daily life. As we know, light is frequently used to measure characteristics of materials and devices, investigate biological samples, and read and record information in an optical disc, such as a compact disc (CD) or a digital versatile disc (DVD). There is a need for a small device size or a miniature device in many applications. For example, optical coherence tomography (OCT) is an optical imaging technology capable of measuring three-dimensional structures of highly scattering biological tissues. A doctor is able to observe beneath a patient's skin using an OCT. Currently, OCT system is bulky and expensive. A miniature OCT will lower the cost and make it possible for a portable or even disposable device, which in turn would expand OCT applications greatly.
External dimensions of an optical device depend upon its opto-mechanical structure, which is determined by the optical structure. An optical device basically comprises a light source, a detector, and other optical components. The light source generates a light beam which is transmitted along an optical path. The detector receives a signal beam which is transmitted through another path. Usually, the two paths overlap partially and are connected by a beam splitter such that they can share some components to make the device compact. In an optical measurement device, for example, a beam from a light source is focused onto a sample by a focusing lens and reflected back, the reflected beam is collected by the focusing lens, and transmitted to a detector. Since the light source and the detector are discrete devices which are disposed in two locations, a beam splitter is needed to split an optical path from the sample to the source, such that part of the reflected beam can follow another path to reach the detector.
Accordingly, there exists a need to reduce or further reduce the size of an optical device; a current optical device, however, consists of at least three components: a light source, a detector, and a beam splitter, which sets a limit for dimension reduction.